The present invention relates to a method for producing material-charged substrates in which
a) at least one substrate is introduced into an evacuated vacuum container;
b) the surface of the substrate to be charged is exposed to a reactive gas which is adsorbed on the surface;
c) the exposure of the surface to the reactive gas is terminated,
d) the reactive gas adsorbed on the surface is allowed to react.
Such a method is prior known from U.S. Pat. No. 5,916,365. Therein a substrate is introduced into an evacuated vacuum container with a container wall comprised of ceramics, delimiting the process volume against the environment.
The surface to be coated of the substrate is exposed to a first reactive gas, which is adsorbed on said surface. The exposure of the surface to the reactive gas is terminated by subsequently pumping off the reactive gas.
A second reactive gas is subsequently introduced and, by means of a coil configuration provided outside of the vacuum container, an electromagnetic high-frequency field is generated in the container. Thereby at least a portion of the introduced second reactive gas is activated to form radicals, and the first reactive gas adsorbed on the surface, is allowed to react exclusively with said radicals generated by the effect of the high-frequency field.
The present invention addresses the problem of proposing a method of the above listed type, which builds on the deposition of a monolayer of atoms on the surface of the substrate to be coated, but has a substantially expanded flexibility of application with respect to the variety of monolayers which can be deposited.
We are herein addressing charging with materials for the reason that said monolayer does not need to be deposited as a continuous layer in the sense of a coating, but rather the density of deposited atoms can be far lower than is necessary for the formation of a continuous layer. But, if desired, the material charging can readily take place such that a continuous monolayer is formed, in this case in the sense of a coating.
This is attained according to the invention thereby that
d1) the surface with the adsorbed reactive gas is exposed to a low-energy plasma discharge with ion energy EI0 on the surface of the substrate of
0 less than EI0xe2x89xa620 eV 
and an electron energy Eeo of
0 eV less than Eeoxe2x89xa6100 eV, 
d2) the adsorbed reactive gas is allowed to react at least with the cooperation of plasma-generated ions and electrons.
In contrast to said U.S. Pat. No. 5,916,365 where the adsorbed gas is exclusively allowed to react with radicals, which by definition are electrically neutral, according to the invention the reactive gas adsorbed on the surface is also allowed to react mildly through the effect of ions and electrons generated by low-energy plasma discharge. Therewith the feasibility is given of properly stabilizing the adsorbed gas also without effect of radicals of a further reactive gas on the surface, solely through xe2x80x9cmildxe2x80x9d interaction with low-energy inert gas ions and electrons or through such effect by other reactive gas ions.
Although the cited U.S. Pat. No. 5,916,365 explains that it was prior known to deposit thin coatings with the inclusion of a glow discharge in an atmosphere of a mixture of reactive gases, but which did not lead to satisfactory coating formation, in the course of the present description it will be explained how the plasma discharge employed according to the invention must be implemented in order, in addition to the generation of the effect of ions and electrons onto the adsorbed reactive gas or gas mixture, to activate in the plasma discharge also a second reactive gas or reactive gas mixture to form radicals and ions and to bring the adsorbed reactive gas or gas mixture additionally into interaction with the radicals generated by plasma activation, and per se electrically neutral radicals, as well as reactive gas ions.
Since in any event electrically charged particles participate in the reaction of the adsorbed gas, the reaction and in particular also its distribution can be controlled by electric and/or magnetic fields, whereby, however, the behavior of radicals alone would not be influenced.
In a preferred embodiment the ion energy EI on the surface of the substrate is further reduced to the range
0 eV less than EIxe2x89xa615 eV. 
Further, the adsorbed reactive gas can also be a reactive gas mixture. The plasma discharge is furthermore, either maintained in an inert gas atmosphere, therein preferably in an argon atmosphere, or the plasma discharge is generated in an atmosphere which contains a further reactive gas or gas mixture. This further reactive gas or gas mixture preferably comprises at least one of the following gases:
hydrogen, nitrogen, oxygen, preferably hydrogen, or it consists of hydrogen gas.
In a further preferred embodiment of the method according to the invention the vacuum container is evacuated to a pressure pv for which applies:
10xe2x88x9211 mbarxe2x89xa6pvxe2x89xa610xe2x88x926 mbar. 
This ensures that virtually no contaminants are deposited from the vacuum atmosphere into which the substrate is introduced, and disturb the surface.
In a further preferred embodiment the reactive gas or gas mixture, which is to be adsorbed on the surface, is introduced up to a partial pressure pp for which applies:
10xe2x88x924 mbarxe2x89xa6ppxe2x89xa61 mbar. 
To a certain extent the quantity of the reactive gas or gas mixture adsorbed on the surface can be controlled by the time period between exposing said surface and terminating this exposure. It is essentially possible therein to assume an exponential function coursing towards a saturation value with a time constant characteristic for the dynamics of the saturating-out. This time constant can therein, if required, be controlled by heating or cooling the surface.
In a further preferred embodiment of the method according to the invention, the exposure of the surface to the reactive gas or reactive gas mixture to be adsorbed is terminated thereby that the substrate is transferred from the evacuated vacuum container with the reactive gas or gas mixture into a further evacuated vacuum container. The remaining process steps are completed in the further evacuated vacuum container. This has the advantage that a first vacuum container serves exclusively for the gas adsorption and therewith remains free of contamination, while the further vacuum container is employed for the plasma discharge reaction of the adsorbed gas.
In this approach it is possible, for example, to provide centrally a further vacuum container for the plasma discharge further treatment of the substrates, which previously had possibly adsorbed different reactive gases or reactive gas mixtures, in the specific xe2x80x9cadsorptionxe2x80x9d container grouped about the central further vacuum container. Therewith complex coating systems comprised of even a multiplicity of different atom monolayers can be built layer by layer.
In many cases for the sequential deposition of differing or identical atomic monolayers in the central plasma reaction container using said low-energy discharge the same second reactive gas or reactive gas mixture can be employed, namely in particular preferred nitrogen and/or hydrogen and/or oxygen, therein in particular preferred is hydrogen. Conversely, it is also possible to assign several of the further vacuum containers for the reaction of the adsorbed reactive gases or gas mixtures in plasmas to an xe2x80x9cadsorptionxe2x80x9d container, namely primarily when the adsorption step is shorter in time than the reaction step in the plasma.
In a further preferred embodiment of the method according to the invention, the exposure of the surface to the reactive gas or reactive gas mixture to be adsorbed is terminated by pumping out the remaining reactive gas or gas mixture from the evacuated vacuum container.
This pumping-out is therein preferably carried out until a total pressure pvxe2x80x2 has been reached in the vacuum container, for which applies:
10xe2x88x9211 mbarxe2x89xa6pvxe2x80x2xe2x89xa610xe2x88x928 mbar. 
Stated differently, for the termination of the reactive gas exposure the same pressure conditions are established again which obtained before the gas exposure, i.e. ultrahigh vacuum conditions.
If, as previously stated, the termination of the adsorption step is realized thereby that the substrate is transferred into a further vacuum container, apart from the partial pressure of the inert gas and/or partial pressure of a second reactive gas or gas mixture, said residual gas ultrahigh vacuum pressure ratios are there also adjusted.
The reaction of the adsorbed reactive gas or gas mixture with the cooperation of plasma-generated ions and electrons is not critical with respect to time due to the use of the low-energy plasma of said type. This process proceeds, at least approximately, again exponentially to an asymptotic value. If the plasma treatment is maintained at least during a predetermined minimum time period, this treatment can subsequently be further maintained without the generated atom monolayer, which in this case is continuous, to be significantly impaired. This has significant advantages for the automation and the timing of the method according to the invention, for example embedded in a complex sequence of additional surface treatment steps.
If the method according to the invention is terminated after the method step d2), depending on the adsorption quantity (exposure time-controlled) and/or quantity of the gas atoms available for the adsorption as well as plasma effect (plasma treatment time and/or intensity) and/or utilization of a second reactive gas or gas mixture (radical and ion formation), an atom monolayer of different density up to a continuous atom monolayer is generated. If no continuous atom monolayer is targeted, the option is given of depositing virtually, in the sense of an implantation or vaccination technique, on the substrate surface or an already deposited continuous atom monolayer only xe2x80x9cisolatedxe2x80x9d atoms of a type identical to those in the base or of a different type or of a different material.
In a further preferred embodiment of this method, at least the method steps b) to d2) are run through at least twice whereby at least two atomic monolayers are deposited one above the other. Therein it is possible to change from monolayer to monolayer the surface-adsorbed reactive gases or gas mixtures, also to employ optionally second applied reactive gases or gas mixtures in the plasma discharge atmosphere, such that as a monolayer intentionally different layers can be deposited. If an epitaxial coating is intended, a hetero-epitaxial coating is generated. If in all layers the same material is deposited, homoepitaxy is generated with epitaxial growth.
Furthermore, it is in principle entirely possible to apply in a preferred embodiment after at least a one-time completion of step d2), be that thus for the first time, or, with repeated-n-passes through cycles b) to d2), a further material onto the surface resulting in this case, and specifically with any one of the known coating methods, be this with vacuum technique, wet chemistry or galvanically.
In a further, in particular preferred, embodiment of the method according to the invention, before said surface is exposed to the reactive gas or reactive gas mixture, this surface is exposed to a low-energy inert gas plasma, preferably an argon plasma, with an ion energy at said surface, for which applies:
0 eV less than EI1xe2x89xa620 eV 
preferably even of
0 eV less than EI1xe2x89xa615 eV 
and at electron energies Ee1 of
0 eV less than Ee1xe2x89xa6100 eV. 
Thereby defined surface conditions are generated at the subsequently gas-adsorbing surface.
In a further preferred embodiment of the method according to the invention, before exposing said surface to the reactive gas or reactive gas mixture to be adsorbed, the surface is exposed to a low-energy plasma discharge in an atmosphere which comprises a further reactive gas, where for the ion energy EI2 on the substrate surface applies:
0 eV less than EI2xe2x89xa620 eV, 
preferably applies
0 eV less than EI2xe2x89xa615 eV 
and at electron energy Ee2 of
0 eV less than Ee2xe2x89xa6100 eV. 
Here, on the one hand, defined surface conditions are also generated on the subsequently gas-adsorbing surface, and, additionally, said surface is cleaned. This takes place in particular with the preferred application, as the further reactive gas, of at least one of the gases hydrogen, nitrogen or oxygen. Especially preferred therein is the use of an atmosphere comprising hydrogen, preferably of an atmosphere which, optionally apart from an inert gas, such as in particular argon, is comprised of hydrogen.
In the following method steps will be considered, which are preferably carried out after the gas adsorption and the reaction of the adsorbed gas.
In an especially preferred embodiment, after the reaction of the adsorbed reactive gas or mixture, the surface is exposed to a low-energy inert gas plasma, preferably an argon plasma, with an ion energy EI3 on the surface of
0 eV less than EI3xe2x89xa620 eV, 
preferably of
0 eV less than EI3xe2x89xa615 eV 
and with an electron energy Ee3 of
0 eV less than Ee3xe2x89xa6100 eV. 
In a further preferred embodiment of the method according to the invention, after said reaction of the adsorbed reactive gas, the surface is exposed to a low-energy plasma discharge in an atmosphere which comprises a further reactive gas or reactive gas mixture, where for the ion energy EI4 on the substrate surface applies:
0 eV less than EI4xe2x89xa620 eV, 
preferably
0 eV less than EI4xe2x89xa615 eV 
and with electron energy Ee4, for which applies
0 eV less than Ee4xe2x89xa6100 eV. 
Preferably as the further reactive gas at least one of the gases hydrogen, nitrogen or oxygen is here also employed, therein using in particular hydrogen.
By reaction of this further reactive gas, simultaneously also the inner surfaces of the vacuum container are cleaned.
If, as was explained above, for the reaction of the adsorbed reactive gas the plasma discharge is also maintained in a reactive gas or reactive gas mixture, in particular with at least one of the gases hydrogen, nitrogen or oxygen, highly preferred with at least a dominant fraction of hydrogen, then simultaneously the inner surfaces of the vacuum container are also cleaned, and specifically faster, cleaner and more defined than would be possible by pumping-out alone.
In particular by selecting the plasma treatment method preceding the reactive gas adsorption, the condition of the subsequently gas-adsorbing surface is at least also influenced. Therewith is also influenced whether or not an epitaxial deposition results, or an amorphous or polycrystalline one in the case of an uncleaned, amorphous, polycrystalline substrate surface. Through the substrate surface temperature the growth characteristic can also be influenced in this respect.
With the method according to the invention for the production of material-charged substrates, in an especially preferred manner the charging takes place by means of at least one of the following materials:
oxides or nitrides or oxinitrides of Si, Ge, Ti, Ta, Hf, Zr, Al, Nb, W and/or of the following metals:
Al, Ti, Cu, W, Ta or mixtures of said materials. Especially preferably said surface charging takes place with at least one of the materials:
silicon oxide, tantalum oxide, zirconium oxide, titanium nitride, tantalum nitride, tungsten nitride, (TaSi)xNy.
In a further, highly preferred embodiment of the method according to the invention, the process atmosphere surrounding the surface of the substrate during at least one of the phases, comprising steps b) and c) and/or d) to d2), is isolated from the inner wall of a vacuum container disposed in the ambient surrounding. Consequently this isolation is carried out either while the surface to be coated is exposed to the reactive gas or gas mixture for adsorptionxe2x80x94until the termination of this exposurexe2x80x94and/or during the reaction of the adsorbed gas.
The fundamental finding is therein that a functional isolation of structures, which ensures the required technical vacuum pressure ratios compared to ambient pressure, on the one hand, and of structures which are directly exposed to the treatment process, on the other hand, in view of the high requirements made of purity and/or optimum integratability of the method according to the invention entails significant advantages in an automated fabrication procedure.
If the surface of a substrate to be charged is being addressed and has been addressed, by that is to be understood also the surface of an already charged or coated substrate. The following example will be discussed for which the method according to the invention is especially suitable:
Let it be assumed that a substrate is coated with a dielectric, in particular SiO2 coating. Through etching steps, which are not of further interest here, channels with a ratio of depth to width of, for example, 1:10 are sunk into the coating comprised of said dielectric materials, for example with a width of 50 nm. These channels are to be filled, for example galvanically, with an electrically conducting material, in particular with copper, in order to form so-called xe2x80x9cinterconnectsxe2x80x9d. The deposition in particular of copper on dielectric surfaces is highly problematic in terms of adhesion. According to the invention onto the surface of the dielectric coatings, including the channels, a liner comprising only a few atom monolayers is deposited as a bonding layer between the dielectric material and the electrically conducting material. Due to its extremely low thickness, it impairs the conductor cross section of said interconnect channels only negligibly. Such bonding layers are known as liner coatings or xe2x80x9cseed layersxe2x80x9d.
In a further preferred embodiment of the method according to the invention the substrate surface (optionally comprising the substrate coating surface) is cleaned before the adsorption step and/or after the reaction of the adsorbed reactive gas or gas mixture, by employing a plasma-enhanced cleaning step in which reactive gas or gas mixture, preferably comprising at least hydrogen, introduced into a cleaning process volume, is activated by means of a low-energy plasma discharge with an ion energy Er on the substrate surface of
0 eV less than Erxe2x89xa620 eV, 
preferably
0 eV less than Erxe2x89xa615 eV 
at an electron energy Eer of
0 eV less than Eerxe2x89xa6100 eV. 
In a preferred embodiment, comprising this at least one cleaning step, of the method according to the invention, during the cleaning step the cleaning process atmosphere is isolated by means of a metallic encapsulation from the inner wall of a cleaning vacuum container at ambient surrounding, orxe2x80x94and this preferablyxe2x80x94this process atmosphere is delimited directly by the inner wall of the cleaning vacuum container at ambient surrounding.
If it is taken into consideration that, as will yet be described, preferably the method phases, applied according to the invention, comprised of the steps b) and c), on the one hand, and/or d) to d2) are carried out in a process atmosphere which is isolated by dielectric material from the conventionally metallic wall, which is at ambient pressure, it is evident that through the latter approach for said cleaning steps more cost-effective solutions can be applied. It must therein be observed that in particular a cleaning step before the initial exposure of the substrate surfaces to the reactive gas or reactive gas mixture to be adsorbed can lead to considerable contamination of the container wall.
As already indicated, in a preferred embodiment a single atom monolayer is deposited onto the surface by a single sequence of steps a) to d2), optionally with specifically adjusted density up to a continuous layer. In a further preferred embodiment by repeating steps b) to d2) a multilayer, for example epitaxial, coating is grown. If in each case the same reactive gas or reactive gas mixture to be adsorbed is employed, with a monocrystalline, cleaned surface, in the case of epitaxial growth this leads to a homoepitaxial coating. If the reactive gas to be adsorbed is changed in each instance after a predetermined number of deposited monolayers, this leads to extremely thin heteroepitaxial coatings.
In a further preferred embodiment of the method according to the invention, after carrying out a predetermined number of passes through steps b) to d2) in particular sequentially on several substrates, the process volume of the vacuum container is subjected to a plasma-enhanced process volume cleaning step without a substrate being introduced or, optionally, with a substrate dummy in the vacuum container, which process volume cleaning step preferably first comprises an etching step, subsequently a cleaning step, preferably in a plasma with hydrogen, an inert gas or a mixture thereof.
In a further preferred embodiment of the method according to the invention, a substrate cleaning step is carried out before step a) and/or after step d2 spatially separated from said vacuum container, wherein the transport of the substrate between said vacuum container and a cleaning container is carried out under vacuum.
It is therein preferred if at least piece-wise, this transport is realized such that it is linear or, especially preferably, along a circular path with linear guide movements to said containers, preferably with movement components which are radial with respect to the circular path.
In a further preferred embodiment of the method according to the invention, the process atmosphere during the phases comprising steps b) and c) and/or d) to d2) is isolated from the inner wall of a vacuum container at ambient surrounding, and specifically by means of a surface, which in the new condition is chemically inert against the reactive gas or gas mixture to be adsorbed and/or against a second plasma-activated reactive gas or gas mixture, preferably by means of a dielectric or graphitic surface.
In a further preferred embodiment the inert surface is layed out as the surface of a partition wall, which along predominant area sections is spaced apart from the inner wall of the vacuum container. The surface for the isolation is preferably realized in the new condition of at least one of the following materials:
quartz, graphite, silicon carbide, silicon nitride, aluminum oxide, titanium oxide, tantalum oxide, niobium oxide, zirconium oxide or a layered combination of these materials, in this case also with diamond-like carbon or diamond.
In a further highly preferred embodiment of the method according to the invention, the plasma discharge is realized with an electron source with an electron energy xe2x89xa650 eV, in particular preferred by means of a DC discharge.
This is preferably attained further by means of a thermionic cathode, preferably by means of a directly heated thermionic cathode.
Thereby that in the process volume of the vacuum container for said plasma discharge preferably at least two spatially offset anodes, preferably each heatable, are provided, preferably each separately electrically actuatable, and the electric potentials connected thereto and/or the anode temperatures are controlled or set, the plasma density distribution along the surface is adjusted or controlled statically or dynamically. In a further preferred embodiment the cathode-anode gap for the plasma discharge is disposed essentially perpendicularly and preferably centrally with respect to said surface.
In a further preferred embodiment of the method according to the invention, during the generation of the plasma discharge a magnetic field is generated in the process volume and the plasma density distribution along the surface is adjusted or controlled stationarily and/or dynamically by means of this field. The plasma density distribution is preferably at least locally wobbled, leading to an effect as if the substrate held stationarily in the plasma were moved with respect to the discharge.
Moreover, preferably at least the reactive gas or gas mixture to be adsorbed is introduced into the process volume such that it is distributed, preferably with an inflow direction substantially parallel to the substrate surface and, further preferred, with injection sites equidistant from the substrate surface. In an especially preferred embodiment of said method, the substrate is formed by a silicon oxide-coated substrate with channels sunk into the silicon layers, wherein after carrying out n-times the step d2) copper is deposited into the channels. In every case n is therein greater than 1.